1. Field of the Invention
The present invention relates to a high-brightness phosphor screen for use in luminescent displays using phosphors, and a method for manufacturing the same, and more particularly, to a phosphor screen capable of emitting light with high brightness at a low or middle level voltage, and a method for manufacturing the same.
2. Description of the Related Art
In luminescent displays, such as cathode ray tubes (CRTs), vacuum fluorescent displays (VFDs), field emission displays (FEDs), phosphor serves to form an image from an electrical signal by emitting light after having been excited by low incident electrons. Phosphor exhibits an intrinsic color depending on its composition, and its color and brightness vary according to the energy and thee number of electrons bombarding the surface of phosphor. Here, the energy and the number of electrons which bombard a phosphor screen are determined by the structure and the operation type of a driving unit.
Until now, research into phosphor has been focused on high-voltage phosphors excitable with a few tens of kilovolts for use in CRTs, and low-voltage phosphors excitable with a few hundred volts for use in VFDs. With an increasing interest in FEDs which are driven by a middle level of voltage of 1-4 kW, there is a need for a phosphor for effective use in such a display with application of a middle level voltage.
When an existing high-voltage phosphor for CRTs is excited with a middle level of voltage, the excitation energy of electrons is lower than with a high voltage, so that a larger electron current than for a CRT is needed to give the same brightness due to reduced luminescent efficiency. However, the application of a high current reduces the lifetime of the phosphor, and thus it would be desirable to increase the luminescent efficiency at a middle level working voltage without increasing the current.
ZnO:Zn phosphors, which are known as a type of phosphor having a high luminescent efficiency at low voltages, emit blueish green light with a major emission peak near 505 nm. For this reason, in spite of the advantage of a high brightness with a low or middle level working voltage and reduced power consumption, ZnO:Zn phosphors are unsuitable for displaying a color image, and thus their applications have been limited to black-and-white image displays.
To increase the driving efficiency at a middle level voltage, i.e., to enhance the brightness at a middle level voltage, U.S. Pat. No. 5,788,881 discloses a method of forming a phosphor screen with a mixture of two phosphors having different conductivities. In particular, the conductivity of the entire phosphor screen is increased using the conductivity of a low-voltage phosphor, thereby enhancing the brightness characteristics.
However, there is still a need for a phosphor applicable in displaying color images with enhanced color purity and high luminescent efficiency at a middle level working voltage.